The invention relates generally to test fixtures, and more specifically to a radio frequency test fixture for testing ball grid array modules.
In combined transmitter and receiver ball grid array (BGA) modules, i.e. BGA radio modules, comprising a radio frequency (RF) input/output (I/O) terminal, that I/O terminal is normally connected directly to an antenna via a corresponding solder ball. Thus, both transmitted and received RF signals are propagated through this terminal.
To keep the cost of BGA modules as low as possible, such RF I/O terminals should not differ from the other terminals of the modules such as digital control signal terminals and voltage supply terminals.
Although the RF or antenna terminals do not differ physically from the other I/O terminals, it is extremely important to ensure proper electrical impedance of such terminals. If the impedance requirements are not met, the transmitted radio signals will be weaker, and the sensitivity of the receiver will be reduced. Proper electrical impedance is a module design criterion.
The impedance of the antenna connection is equally important. A user of the radio module has to design the connection between the module and the antenna such that the electrical impedance is matched to the module.
This issue imposes a problem associated with test and measurement of the module in that the module, during testing, has to be connected to the test system via an interconnect system having proper impedance.
The object of the invention is to bring about a RF test fixture for testing BGA radio modules ensuring proper impedance matching between the modules and the test system.
This is attained by means of the RF test fixture in accordance with the invention in that it comprises a number of standard spring-loaded probes in sleeves fixed between two printed circuit boards in such a manner that the ends of the sleeves are flush with the respective outward-facing surface of the printed circuit boards, the ends of the sleeves with a probe for contacting a solder ball connected to module ground being grounded, and at least one electrically conducting impedance-matching element extending between the printed circuit boards adjacent to and in parallel with a sleeve with a probe for contacting a solder ball connected to an RF I/O terminal on the module for impedance matching purposes. The ends of each such impedance-matching element being grounded.
Hereby, proper impedance matching can be obtained between the BGA module and the test system.